This invention relates to polyesterimide resin compositions which are soluble in water-based solvents. These compositions are used as coatings, particularly as wire enamel.
Wire enamels designed for severe service in continuous operation at temperatures above 220.degree. C. have been aromatic polyimide and polyamide-imide compositions. These compositions require nitrogen or sulfoxide-containing organic polar solvents which are expensive and present problems in disposal. The polymeric amide-imide-ester wire enamals described in Sattler, U.S. Pat. No. 3,555,113 (1971) are an attempt to accept moderate compromise in thermal properties in order to reduce the cost of the required solvent. But even these compositions require aromatic solvents such as cresol, cresylic acid, phenol, and hydrocarbon diluents which still represent considerable expense and disposal in a commercial operation.
Weddleton, U.S. Pat. No. 3,853,817 (1974) teaches preparation of thermosetting polyesterimide resins suitable for electrostatic spraying deposition upon electrical conductors, but the imide portion of these resins is once again formed by reaction in the expensive nitrogen and sulfoxide solvents.